JP2011046236A - Control device of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an electric power steering device allowing obtaining of suitable steering feeling, even when steering is rotated at high speed, etc. <P>SOLUTION: When the effect that a ωI control is under execution is determined, even when the effect that a field weakening condition (saturation factor S>saturation factor decision threshold Sh) is not established during execution of a field weakening control, the execution of the field weakening control is continuously performed without being released. As a result, generation of the so-called vibration control alternately repeating operations and executions by the field weakening control and the ωI control is avoided, and thereby smooth steering is maintained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an electric power steering device that applies an assist force (steering assist force) by a motor to a steering system of a vehicle such as an automobile.

  2. Description of the Related Art Conventionally, as a control device for this type of electric power steering apparatus, one that drives and controls a motor based on a vehicle speed detected through a vehicle speed sensor and a steering torque detected through a torque sensor is well known. The driving force (rotational force) of this motor is transmitted as a steering assisting force to the steering shaft or the rack shaft via a speed reduction mechanism composed of gears or the like, thereby assisting the steering operation. The motor is driven and controlled through switching driving of a motor driving circuit including a plurality of switching elements.

  A brushless motor is often used as the motor. The control device performs coordinate conversion of the detected values of the three-phase current sensor from three phases to two phases (d / q axes), and performs current feedback control in the d / q axis coordinate system. Since the d / q axis coordinate system is a rotational coordinate system, current vector control is performed by dividing the current into a torque component and a field weakening component. In the electric power steering apparatus, there is a case where the motor rotation is required in a high speed region exceeding the base speed, for example, when a quick steering operation is performed. In this high-speed region, the induced voltage becomes higher than the power supply voltage, and a so-called voltage saturation state in which no current can flow occurs. In order to prevent this, the d-axis current command value in the current feedback control is set to a negative value corresponding to the rotation speed of the motor (in other words, the steering speed of the steering), that is, the d-axis current is caused to flow by flowing a negative d-axis current. Field weakening control is generally performed to reduce the magnetic flux in the direction and reduce the induced voltage. Through execution of such field weakening control, the motor rotation range (operating range) is expanded to a high speed range exceeding the base speed, and the followability at high speed steering is ensured. Patent Document 1 describes an electric power steering device that rotationally drives a brushless motor by field-weakening control when the rotation speed of a brushless motor for assisting steering reaches a predetermined range.

  In addition to the field-weakening control described above, the applicant of the present invention is a control device for an electric power steering apparatus that performs so-called ωI control that limits the q-axis current command value (Iq) according to the rotational speed (ω) of the motor. We are considering hiring. This so-called ωI control is performed for the purpose of suppressing the current drawn from the battery and adding weight to the steering by adapting the steering torque. For example, when the rotational speed of the motor increases, the control device decreases the q-axis current command value according to the rotational speed. As a result, the value of the current command value calculated as the control target amount of the steering assist force decreases, and the value of the duty (on duty) corresponding to each phase of the motor calculated based on the current command value also decreases. As a result, the steering assist force by the motor is also reduced, and the steering is given a weight according to the steering speed.

  Here, the motor output characteristics (performance without ωI control) indicated by the relationship between the motor torque and the motor rotation speed are shown in the graph of FIG. When the vertical axis represents the vertical axis, as indicated by the solid line in the figure, there is a characteristic that the rotational speed gradually decreases as the motor torque increases. On the other hand, the characteristics required on the vehicle side are significantly lower than the output performance of the original motor, particularly in the high rotation speed region and the high torque region, as shown by the white circle in the figure. That is, the high rotation speed region or the high torque region indicated by hatching in the graph of FIG. By performing the above-described ωI control, by cutting the region that is the target of power limitation, it becomes possible to bring the output performance of the motor closer to the performance required by the vehicle.

JP 2002-345281 A

  However, when the above-described field weakening control and ωI control are executed together, there are the following concerns. In other words, field weakening control is control that attempts to decrease the value of the d-axis current command value as the motor speed increases, and ωI control attempts to decrease the value of the q-axis current command value as the motor speed increases. This is the control. Thus, both the field weakening control and the ωI control depend on the rotational speed of the motor, in other words, the steering speed (ω) of the steering.

  For this reason, when attempting to steer at high torque and high speed, it is determined that the switching duty of the motor drive circuit has reached its upper limit (that is, the voltage is saturated), and field weakening control is executed. As a result, although high-speed steering is possible, when the operating state of the motor enters the operation region of the ωI control (the region indicated by hatching in the previous graph of FIG. 6), the q-axis current command value through the execution of the ωI control, As a result, the value of the current command value decreases and the switching duty of the motor drive circuit decreases. Along with this, the output state of the motor is weakened, and the operating condition of the field control is removed, and the steering becomes heavy. When such a cycle is entered, there is a possibility that smooth steering of the steering may be hindered by the above-described field weakening control and ωI control interfering with each other. For example, when the steering operation is performed, a feeling of being pulled out once is generated, which leads to a decrease in steering feeling or a feeling of strangeness.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an electric power steering device that can obtain a suitable steering feel even when the steering is rotated at high speed or the like. It is to provide.

  According to the first aspect of the present invention, the d-axis current command value and the q-axis current command value in the dq coordinate system are calculated as the current command values for the three-phase motor that generates the steering assist force. Electric power for converting a phase current value into a d-axis current value and a q-axis current value in the dq coordinate system, and performing feedback control so that these values follow the d-axis current command value and the q-axis current command value In the control device of the steering device, when it is determined that a specific operation condition is established with a first calculation unit that executes ωI control that limits the value of the q-axis current command value according to the rotation speed of the motor And a second computing unit that executes field weakening control that sets the d-axis current command value to a negative value in accordance with the rotational speed of the motor, and the operation condition of the control is non-executed during execution of the field weakening control. It is established If it is determined that the ωI control is being executed by the first arithmetic unit, the field weakening control is continuously executed when it is determined that the ωI control is being executed. This is the gist.

  According to this configuration, even when it is determined that the operating condition of the field weakening control is not established while the field weakening control is being executed, the field weakening control is continued when it is determined that the ωI control is being executed. Execute. For this reason, the occurrence of so-called control vibration, in which the field-weakening control and the ωI control are alternately executed and stopped alternately, is avoided. Therefore, smooth steering of the steering is maintained.

  According to a second aspect of the present invention, in the control device for the electric power steering device according to the first aspect, it is determined that the operating condition of the control is not established during execution of field weakening control by the second arithmetic unit. When it is determined that the execution of the ωI control by the first calculation unit is stopped, the motor rotation speed and the q-axis current value are each waited for a value less than a specific threshold value. Therefore, the gist is to cancel the execution of the field weakening control by the second arithmetic unit.

  According to this configuration, when it is determined that the operation condition of the field weakening control is not established during the execution of the field weakening control, the rotation speed of the motor is determined when the execution of the ωI control is determined to be stopped. And after waiting for the q-axis current value to be less than a specific threshold value, the execution of the field weakening control is canceled. Since the execution of both the ωI control and the field weakening control is not canceled at a stretch, a sudden change in the steering assist force is suppressed. For this reason, a suitable steering feel of the steering is maintained.

  According to a third aspect of the present invention, in the control device for the electric power steering apparatus according to the first or second aspect, the field-weakening control by the second arithmetic unit when the ωI control is performed by the first arithmetic unit. The gist is to execute the ωI control only when it is determined whether or not there is a possibility that the field weakening control will be executed.

  According to this configuration, when there is a possibility that field weakening control is executed, field weakening control is executed in preference to ωI control. For this reason, the smooth steering feel of the steering is ensured by enabling the high speed steering and avoiding the interference of the ωI control and the field weakening control.

  According to the present invention, a suitable steering feel can be obtained even when the steering is rotated at a high speed or the like.

The schematic block diagram of an electric power steering apparatus. The control block diagram which shows the electric constitution of the said apparatus. The flowchart which shows the process sequence of steering assistance control. The flowchart which shows the process sequence of (omega) I control. The flowchart which shows the process sequence of field weakening control. NT characteristic figure which shows the cancellation | release permission area | region of field weakening control.

  Hereinafter, a first embodiment in which the present invention is embodied in a so-called column-type electric power steering device (EPS) in which a power assist unit and its control device are provided in a steering column will be described with reference to FIGS. This will be described based on the flowchart of FIG.

<Outline of electric power steering device>
First, a schematic configuration of the electric power steering apparatus will be described. As shown in FIG. 1, in the electric power steering apparatus 1, a steering shaft 3 that rotates integrally with the steering wheel 2 is connected in order of a column shaft 8, an intermediate shaft 9, and a pinion shaft 10 from the steering wheel 2 side. The pinion shaft 10 is meshed with a rack portion 5a of a rack shaft 5 provided orthogonal to the pinion shaft 10. The rotation of the steering shaft 3 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4 including the pinion shaft 10 and the rack portion 5a. The reciprocating linear motion is transmitted to a knuckle arm (not shown) via tie rods 11 connected to both ends of the rack shaft 5, thereby changing the steering angle of the steered wheels 12.

  In addition, the electric power steering device 1 includes a steering force assist device (power assist unit) 22 that applies an assist force for assisting a steering operation to the steering system, and an electronic control device that controls the operation of the steering force assist device 22 ( ECU) 23.

  A motor 21 that is a drive source of the steering force assisting device 22 is operatively connected to the column shaft 8 via a speed reduction mechanism 24 formed of a gear or the like. The rotational force of the motor 21 is decelerated by the speed reduction mechanism 24 and this is transmitted as an assist force to the steering system, more precisely to the column shaft 8. The electronic control unit 23 controls the assist force as follows. That is, the electronic control unit 23 acquires the vehicle speed V through the vehicle speed sensor 27 provided on the steered wheels 12 and the like. Further, the electronic control unit 23 acquires the steering torque τ applied to the steering wheel 2 and the steering angle (rotation angle) θs of the steering wheel 2 through the torque sensor 28 and the steering angle sensor 29 provided on the column shaft 8. . The electronic control unit 23 calculates a target assist force based on the vehicle speed V, the steering torque τ, and the steering angle θs, and performs power feeding control of the motor 21 to generate the calculated target assist force. The assist force applied to the steering system is controlled through the power supply control of the motor 21. In this example, a brushless motor is employed as the motor 21. The motor 21 rotates by receiving supply of three-phase (U, V, W) driving power from the electronic control unit 23.

<Electrical configuration>
Next, the electrical configuration of the electric power steering device will be described.
As shown in FIG. 2, the electronic control unit 23 supplies a three-phase drive power to the motor 21 based on the microcomputer 31 that generates the motor control signal and the motor control signal generated by the microcomputer 31. And a motor drive circuit 32.

  The motor drive circuit 32 is a known PWM inverter in which three arms corresponding to each phase are connected in parallel with a switching element such as a pair of field effect transistors (FET) connected in series as a basic unit (arm). It is. The motor control signal generated by the microcomputer 31 defines the on-duty of each switching element constituting the motor drive circuit 32. A motor control signal is applied to the gate terminal of each switching element, and each switching element is turned on / off in response to the motor control signal, so that a DC voltage of a vehicle power source (not shown) such as a battery is three-phase (U, V, W) is converted to drive power and supplied to the motor 21.

  The microcomputer 31 includes current sensors 21u, 21v, and 21w that detect phase current values Iu, Iv, and Iw supplied to the motor 21, and a rotation angle sensor 21a that detects the rotation angle θ (electrical angle) of the motor 21. Become connected. The microcomputer 31 uses the d-axis corresponding to the target assist force based on the phase current values Iu, Iv, Iw and the rotation angle θ of the motor 21 detected through these sensors, and the steering torque τ and the vehicle speed V described above. The current command value Id * and the q-axis current command value Iq * are calculated. The microcomputer 31 performs feedback control for causing the d-axis current value Id and the q-axis current value Iq, which are actual currents, to follow the d-axis current command value Id * and the q-axis current command value Iq *.

<Detailed explanation of microcomputer>
Next, the configuration of the microcomputer 31 will be described in detail.
As shown in FIG. 2, the microcomputer 31 includes a basic assist calculator 41, a subtractor 42, a ω converter 43, a two-phase converter 44, an ωI control calculator 45, a field weakening control calculator 46, and a PI calculator 47. A three-phase converter 48, a duty calculator 49, and a motor control signal output unit 50 are provided. Each unit represents various arithmetic functions based on various control programs stored in a nonvolatile memory (not shown) of the microcomputer 31 as a block. The calculation result of each part is temporarily stored in a volatile memory (not shown). Hereinafter, an outline of arithmetic processing executed in each part of the microcomputer 31 will be described.

<Basic assist calculation unit>
The basic assist calculation unit 41 calculates a basic assist current value I0 based on the steering torque τ acquired through the torque sensor 28 and the vehicle speed V acquired based on the vehicle speed sensor. Specifically, the basic assist current value I0 having a larger absolute value is calculated as the acquired steering torque τ (more precisely, its absolute value) is larger and the vehicle speed V is smaller. The basic assist calculation unit 41 outputs the calculation result to the subtracter 42. This basic assist current value I0 is a q-axis current command value when ωI control described later is not executed.

<Ω conversion part>
The ω conversion unit 43 converts the rotation angle θ of the motor 21 acquired through the rotation angle sensor 21a into a rotation speed (steering speed) ω.

<Two-phase converter>
The two-phase conversion unit 44 calculates the phase current values Iu, Iv, Iw of the motor 21 acquired through the current sensors 21u, 21v, 21w based on the rotation angle of the motor 21 detected by the rotation angle sensor 21a. Conversion (d / q conversion) into a d-axis current value Id and a q-axis current value Iq in the d / q coordinate system.

<ΩI control calculation unit>
The ωI control calculation unit 45 performs ωI control that limits the q-axis current command value Iq * based on the rotational speed ω of the motor 21 acquired through the ω conversion unit 43. That is, the ωI control calculation unit 45 calculates the q-axis current limit value Iq_lim based on the motor 21 and the rotational speed ω, and the calculated q-axis current limit value Iq_lim and the basic assist current calculated by the basic assist calculation unit 41. Based on the comparison result with the value I0, it is determined whether or not it is necessary to limit the basic assist current value I0. The ωI control calculation unit 45 outputs the calculated q-axis current limit value Iq_lim to the subtractor 42 only when it is determined that the basic assist current value I0 needs to be limited. Further, the ωI control calculation unit 45 sets an operation flag based on whether or not the ωI control is executed, and outputs a signal indicating the on / off state of the operation flag to the field weakening control calculation unit 46 described later.

<Subtractor>
The subtractor 42 calculates the q-axis current command value Iq * based on the basic assist current value I 0 calculated by the basic assist calculation unit 41 and the calculation result of the ωI control calculation unit 45. When the ωI control is executed by the ωI control calculation unit 45, that is, when the q-axis current limit value Iq_lim is input from the ωI control calculation unit 45, the subtractor 42 is changed from the basic assist current value I0 to the q-axis current limit value Iq_lim. Is subtracted and the result is calculated as the q-axis current command value Iq *. When the ωI control is not executed by the ωI control calculation unit 45, that is, when the q-axis current limit value Iq_lim is not input from the ωI control calculation unit 45, the basic assist current value I0 is directly calculated as the q-axis current command value Iq *. .

<Weak field control calculation unit>
The field weakening control calculation unit 46 executes field weakening control in which the d-axis current command value Id * is a negative value in accordance with the rotational speed ω of the motor 21 generated by the ω conversion unit 43. More specifically, as the rotational speed ω increases, the counter electromotive force generated in the motor coil of each phase also increases. However, the rotational speed of the motor 21 has an upper limit (base speed). However, a negative value of the d-axis current command value Id *, that is, a negative d-axis current is caused to flow to reduce the d-axis direction magnetic flux by utilizing the demagnetizing magnetomotive force due to the d-axis armature reaction. The voltage can be kept low. As a result, the operating range (rotation region) of the motor 21 can be expanded to a high speed region exceeding the base speed.

  The field weakening control calculation unit 46 saturates the switching duty of each switching element (FET) in the motor drive circuit 32 based on the d-axis current value Id and the q-axis current value Iq generated by the two-phase conversion unit 44. Whether or not a voltage saturation state has occurred is determined, and whether or not the above-described field weakening control needs to be performed is determined based on the determination result. In this example, the field weakening control calculation unit 46 sets the d-axis current command value Id * to “0” (Id * = 0) when the field weakening control is not performed.

<PI (F / B) calculation unit 47>
The PI (proportional-integral) calculating unit 47 calculates the difference between the q-axis current command value Iq * and the q-axis current value Iq, the q-axis current deviation ΔIq, the d-axis current command value Id *, and the d-axis current value Id. The d-axis current deviation ΔId, which is the difference value between the two, is calculated. The PI calculation unit 47 multiplies the calculated q-axis current deviation ΔIq and d-axis current deviation ΔId by a predetermined feedback gain (PI gain), thereby obtaining a d-axis voltage command value Vd * and a q-axis voltage command value. Vq * is calculated.

<Three-phase converter>
The three-phase converter 48 converts the d-axis voltage command value Vd * and the q-axis voltage command value Vq * into three-phase voltage command values Vu *, Vv *, Vw * according to the rotation angle θ of the motor 21. To do.

<Duty calculation unit>
The duty calculator 49 generates duty command values Du, Dv, Dw corresponding to the voltage command values Vu *, Vv *, Vw *.

<Motor control signal output unit>
The motor control signal output unit 50 generates a motor control signal having a duty ratio (on duty) defined by each duty command value Du, Dv, Dw. The motor control signal output unit 50 controls the driving of the motor drive circuit 32 and the supply of electric power to the motor 21 through the supply of the motor control signal to each switching element (more precisely, the gate terminal).

<Operation of control device of electric power steering device>
Next, a processing procedure of steering assist control by the electric power steering apparatus configured as described above will be described with reference to the flowchart of FIG. The flowchart is a main routine of steering assist control, and is executed according to various control programs stored in a nonvolatile memory (not shown) of the microcomputer 31.

<Steering assist control>
As shown in FIG. 3, the microcomputer 31 reads a torque signal (steering torque τ) and a vehicle speed signal (vehicle speed V) (step S101), and calculates a basic assist current value I0 based on these torque signal and vehicle speed signal. (Step S102).

  Next, the microcomputer 31 executes ωI control (step S103), and determines the q-axis current command value Iq * by adding the execution result of the ωI control to the basic assist current value I0 calculated previously (step S103). S104). The processing procedure of the ωI control will be described in detail later.

  Next, the microcomputer 31 reads the q-axis current value Iq and the d-axis current value Id calculated by the two-phase conversion unit 44, and the rotation angle θ of the motor 21 detected by the rotation angle sensor 21a (step S105). .

  The microcomputer 31 executes field weakening control based on the q-axis current value Iq, the d-axis current value Id, and the like (step S106), and calculates the d-axis current command value Id * based on the control result. The processing procedure of the field weakening control will be described in detail later.

  Next, the microcomputer 31 executes PI calculation (step S107). That is, the q-axis current deviation ΔIq which is the difference between the q-axis current command value Iq * and the q-axis current value Iq, and the d-axis current which is the difference between the d-axis current command value Id * and the d-axis current value Id. The deviation ΔId is calculated.

  The microcomputer 31 calculates the duty ratio of the motor control signal supplied to the motor drive circuit 32 based on the calculated q-axis current deviation ΔIq and d-axis current deviation ΔId (step S108).

  Thereafter, the microcomputer 31 repeats the processes of steps S101 to S108 at a predetermined control cycle. The motor drive circuit 32 operates based on a motor control signal generated by the microcomputer 31. Thereby, the motor 21 is driven so that a steering assist force (assist force) corresponding to the steering torque τ and the vehicle speed V is applied to the steering system.

<ΩI control>
Next, the processing procedure of ωI control will be described with reference to the flowchart of FIG. The ωI control is executed when the process proceeds to step S103 in the flowchart of FIG. 3 as a subroutine process in the main routine of the steering assist control. The ωI control is a control for executing current limitation on the motor 21 based on the rotational speed ω (steering speed of the steering) of the motor 21.

  When executing the ωI control, the microcomputer 31 first reads the rotational speed ω of the motor 21 calculated by the ω conversion unit 43 (step S201), and calculates the q-axis current limit value Iq_lim based on the rotational speed ω (step S201). S202). The q-axis current limit value Iq_lim is determined based on a power limit map stored in the nonvolatile memory of the microcomputer 31. This map defines the relationship between the rotational speed ω of the motor 21 and the q-axis current limit value Iq_lim, and is set in advance by simulation or the like.

  Next, the microcomputer 31 reads the basic assist current value I0 calculated by the basic assist calculation unit 41 (step S203). The microcomputer 31 compares the basic assist current value I0 with the q-axis current limit value Iq_lim calculated in the previous step S202 (step S204).

  The microcomputer 31 does not execute the ωI control when it is determined that the q-axis current limit value Iq_lim is greater than or equal to the basic assist current value I0 (NO in step S204). Then, the microcomputer 31 sets the operation flag for ωI control to the off state, and ends the processing related to the subroutine. This is for giving priority to the execution of field weakening control described later. That is, in this case, there is a possibility that the switching duty of the motor drive circuit 32 has reached the upper limit value, that is, the voltage saturation state described above.

  On the other hand, when it is determined that the q-axis current limit value Iq_lim is smaller than the basic assist current value I0 (YES in step S204), the microcomputer 31 executes ωI control. In this case, the switching duty of the motor drive circuit 32 has reached the upper limit value, that is, there is little possibility of the above-described voltage saturation state. The microcomputer 31 turns on the operation flag to indicate execution of ωI control (step S206), and outputs the q-axis current limit value Iq_lim calculated in the previous step S202 to the main routine (step S207). ), The process related to the subroutine ends.

  Thus, a series of processes related to ωI control is completed. Thereafter, each time the processing shifts to step S103 in the flowchart of FIG. 3 which is the main routine, the processing of step S201 to step S207 is executed.

<Weak field control>
Next, the processing procedure of field weakening control will be described with reference to the flowchart of FIG. The field weakening control is executed as a subroutine process in the main routine of the steering assist control when the process proceeds to step S106 in the flowchart of FIG. The field weakening control is executed when the followability of the steering assist operation may be reduced due to voltage saturation or the like. As described above, the voltage saturation means a state in which the required output voltage exceeds the maximum voltage (for example, power supply voltage) that can be applied to the motor drive circuit when the motor 21 rotates at high speed.

  When the field weakening control is executed, the microcomputer 31 first determines whether or not the duty ratio of the motor control signal has reached the upper limit value. Specifically, the microcomputer 31 compares the values of the saturation rate S (%) of the output voltage of the motor drive circuit 32 and the saturation rate determination threshold Sh (%) (step S301).

The microcomputer 31 calculates the saturation rate S of the output voltage based on the d-axis current value Id and the q-axis current value Iq generated by the two-phase converter 44, as shown in the following equation.
S = √ (Iq ² + Id ² )
Further, the saturation rate determination threshold Sh differs depending on the running state of the vehicle, the rotational speed ω of the motor 21, and the like, and is approximately 80% or more (eg, 93%).

  If the microcomputer 31 determines that the calculated saturation rate S is greater than the saturation rate determination threshold Sh (YES in step S301), the microcomputer 31 determines the d-axis current based on the rotational speed ω of the motor 21. The command value Id * is calculated based on a known arithmetic expression. Then, the microcomputer 31 outputs the calculated d-axis current command value Id * to the main routine for steering assist control (step S302), and ends the processing related to the subroutine.

  On the other hand, if the microcomputer 31 determines that the calculated saturation rate S is not larger than the saturation rate determination threshold Sh (NO in step S301), the microcomputer 31 proceeds to step S303. .

In step S303, it is determined whether or not the absolute value of the previous d-axis current command value Id * is greater than 0 (zero).
If the microcomputer 31 determines that the absolute value of the previous d-axis current command value Id * is not greater than 0 (NO in step S303), the microcomputer 31 ends the processing related to the subroutine. Here, the case where the absolute value of the previous d-axis current command value Id * does not become larger than 0 is basically only when the field-weakening control is not executed. As described above, this is because, in this example, when the field weakening control is not executed, the value of the d-axis current command value Id * is set to 0. Therefore, in this case (NO in step S303), the microcomputer 31 determines that the execution of the field weakening control has been released.

  On the other hand, when the microcomputer 31 determines that the absolute value of the previous d-axis current command value Id * is greater than 0 (YES in step S303), field weakening control is being executed. The process proceeds to step S304.

  In step S304, the microcomputer 31 determines whether or not the ωI control is executed. If it is determined that the execution flag of the ωI control is in the on state (NO in step S304), the microcomputer 31 determines that the ωI control is being executed and proceeds to the previous step S302. Then, the microcomputer 31 calculates the d-axis current command value Id * in the same manner as described above, and ends the processing related to the subroutine. That is, even if it is determined that the operating condition of the field weakening control (S> Sh in this example) is not established, the execution of the field weakening control is not canceled when it is determined that the ωI control is being executed. It continues as it is.

  On the other hand, when it is determined that the execution flag of the ωI control is in the off state (YES in step S304), the microcomputer 31 determines that the ωI control is not executed and shifts the process to step S305.

  In step S <b> 305, the microcomputer 31 determines whether to cancel the execution of the field weakening control based on the output (= torque × rotational speed) of the motor 21. That is, the microcomputer 31 determines whether or not the output of the motor 21 is a value within the release permission area Ac shown in the NT characteristic diagram of FIG. The release permission region Ac is set to an output region below the NT characteristic curve when the d-axis current command value Id * is 0 (zero), that is, when the field weakening control is not executed. Further, the release permission area Ac is set to an area having a field weakening effect, that is, an area outside the high torque area.

  The microcomputer 31 determines that the output of the motor 21 is within the release permission area Ac based on the rotation speed (number of rotations) ω of the motor 21 and the q-axis current value Iq that is the torque component of the power (current) supplied to the motor 21. Judge whether it is a value or not.

The release permission area Ac is set by the following two conditional expressions.
・ "Ω <B" and "Iq <C"
・ "Ω <D" and "Iq <E"
However, B is a 1st rotation speed determination threshold value, D is a 2nd rotation speed determination threshold value. C is a first torque determination threshold, and E is a second torque determination threshold. The first and second rotational speed determination thresholds B and D and the first and second torque determination thresholds C and E are set in advance based on the motor specifications, required output, and the like. The magnitude relationship between the first and second rotational speed determination thresholds B and D and the first and second torque determination thresholds C and E in these conditional expressions is as follows.

・ D <B,
・ C <E
If it is determined that neither of the two conditional expressions is satisfied (NO in step S305), the microcomputer 31 continues execution of the field weakening control as it is. That is, the microcomputer 31 shifts the process to step S302, calculates the d-axis current command value Id * as described above, and ends the process related to the subroutine.

  On the other hand, when it is determined that one of the two conditional expressions is satisfied (YES in step S305), the microcomputer 31 cancels the execution of the field weakening control (step S306). That is, in this case, the microcomputer 31 does not calculate the d-axis current command value Id *, and the d-axis current command value Id * is a value determined to be used when field-weakening control is not performed. A certain “0” is assumed.

  Thus, a series of processes related to field weakening control is completed. Thereafter, each time the processing shifts to step S106 in the flowchart of FIG. 3 which is the main routine, the processing of step S301 to step S306 is executed.

  In this way, after the field weakening control is executed, the field weakening control permission state is maintained unless the output of the motor 21 decreases to the output in the field weakening control release permission region Ac described above. When the output of the motor 21 becomes a value within the release permission area Ac, the execution of the above-described ωI control is stopped. This is because the release permission area Ac is out of the ωI control operation area indicated by hatching in the graph of FIG. As shown in the graph of FIG. 6, a slight margin is provided between the ωI control operation area and the release permission area Ac. That is, the field weakening control is not stopped immediately after the execution of the ωI control is stopped. In other words, after the execution of the ωI control is stopped, the execution of the field weakening control is stopped after waiting for the output of the motor 21 to fall to the output value in the release permission area Ac. For this reason, the execution of the two controls, the ωI control and the field weakening control, is not continuously stopped. Therefore, a sudden change in steering assist force, and in turn, an uncomfortable feeling during the steering operation can be suppressed.

  For example, when the execution of the ωI control is stopped, the steering assist force increases and the steering feel of the steering becomes light. On the other hand, when the execution of the field weakening control is stopped, the steering feel of the steering becomes heavy. For this reason, if both the ωI control and the field weakening control are stopped at the same timing, the steering feel becomes strange at the timing when it feels that the steering operation has become lighter. May occur. According to this example, occurrence of such an uncomfortable feeling of steering feeling is suitably suppressed.

  Conventionally, when the field weakening control and the ωI control are executed together, there is a concern about the following problems. That is, as described above, when attempting to steer at high torque and high speed, it is determined that the duty ratio of the motor control signal has reached its upper limit (so-called voltage saturation state), and field weakening control is executed. . As a result, although high-speed steering is possible, when the operation state of the motor 21 enters the operation region of ωI control (region indicated by hatching in the previous graph of FIG. 6), the q-axis current command value is obtained through execution of ωI control. Iq * decreases and the switching duty value of the motor drive circuit 32 decreases. Accordingly, the operating condition of the field weakening control (in this example, “saturation rate S> saturation rate determination threshold Sh”) is removed, and the steering becomes heavy. When entering such a cycle, that is, when a so-called control vibration is generated in which ωI control and field-weakening control alternately repeat operation and stop, smooth steering may be hindered.

  In this point, in this example, after the field weakening control is once executed, even when the field weakening control operation condition (saturation rate S> saturation rate determination threshold Sh) is deviated, when the ωI control is executed, The field weakening control is continuously executed. For this reason, the occurrence of the problem that the field weakening control and the ωI control described above interfere with each other is avoided.

<Effect of Embodiment>
Therefore, according to the present embodiment, the following effects can be obtained.
(1) During the execution of the field weakening control, even if the field weakening condition (saturation rate S> saturation rate determination threshold Sh) is not satisfied, it is determined that the ωI control is being executed, the field weakening control is continued. And execute. For this reason, the occurrence of so-called control vibration, in which the field weakening control and the ωI control are alternately repeated in operation and execution, is avoided. Therefore, smooth steering of the steering is maintained.

  (2) When it is determined that the execution of the ωI control is stopped when the field weakening condition is not satisfied during execution of the field weakening control, the output value of the motor 21 is reduced to a value within the release permission area Ac. After waiting for this, the execution of field weakening control was canceled. Thus, both the ωI control and the field weakening control are not turned off at once, and a sudden change in the steering assist force is suppressed. Therefore, a suitable steering feel of the steering is maintained.

  (3) When executing the ωI control, the presence or absence of voltage saturation is determined based on the magnitude relationship between the q-axis current limit value Iq_lim and the basic assist current value I0, and it is determined that there is a possibility of voltage saturation. In this case, the ωI control is not executed. That is, when there is a possibility that field weakening control is executed, field weakening control is executed in preference to ωI control. For this reason, the smooth steering feel of the steering is ensured by enabling the high speed steering and avoiding the interference of the ωI control and the field weakening control.

<Other embodiments>
The embodiment described above may be modified as follows.
-The process of step S204 in the flowchart of FIG. 4, that is, the process for determining whether or not to execute the ωI control may be omitted. Even in this case, smooth steering of the steering is maintained. In other words, even when the field weakening condition is not satisfied during execution of the field weakening control, when it is determined that the ωI control is being performed, the field weakening control is continuously executed. For this reason, the occurrence of so-called control vibration, in which the field weakening control and the ωI control are alternately repeated in operation and execution, is avoided.

  The process of step S305 in the flowchart of FIG. 5, that is, the determination of whether or not the output of the motor 21 is a value within the field-weakening control release permission area Ac may be omitted. That is, in the flowchart of FIG. 5, if it is determined that the determination result in step S304 is not during execution of ωI control, execution of field weakening control is immediately canceled. Even in this case, since the interference between the field weakening control and the ωI control is avoided, the occurrence of the vibrations of both controls described above is basically avoided.

The power assist unit and its control device may be embodied in a so-called rack drive type electric power steering device provided coaxially with the rack shaft 5.
<Other technical ideas>
Next, the technical idea that can be grasped from the above embodiment will be added below.

  The control apparatus for an electric power steering apparatus according to any one of claims 1 to 3, wherein the motor is a brushless motor.

  In the control device for the electric power steering apparatus according to claim 3, the ωI control by the first calculation unit is performed by using a basic assist current value (basic q-axis current command value) calculated based on the steering torque and the vehicle speed. It is limited by the q-axis current limit value calculated according to the rotation speed of the motor, and the determination of the possibility of the field weakening control being executed by the second arithmetic unit is based on the basic assist current value. If the q-axis current limit value is compared with the q-axis current limit value and it is determined that the q-axis current command value is smaller than the basic assist current value, there is a possibility that the field-weakening control is executed. A control device for an electric power steering device that judges that there is no. As described above, it is possible to determine whether or not the field weakening control is likely to be executed through a comparison between the basic assist current value and the q-axis current limit value.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 21 ... Motor, 23 ... Electronic control unit, 45 ... omega I control calculating part (1st calculating part), 46 ... Weak field control calculating part (2nd calculating part).

Claims (3)

A d-axis current command value and a q-axis current command value in a dq coordinate system are calculated as current command values for a three-phase motor that generates a steering assist force, and the detected current values of each phase of the motor are calculated in the dq coordinate system. In a control device for an electric power steering apparatus that converts the d-axis current value and the q-axis current value to a value to follow the d-axis current command value and the q-axis current command value.
A first calculation unit that executes ωI control that limits the value of the q-axis current command value according to the rotation speed of the motor, and the rotation speed of the motor when it is determined that a specific operation condition is satisfied. And a second calculation unit that executes field-weakening control in which the d-axis current command value is a negative value.
When it is determined that the operating condition of the control is not established during execution of the field weakening control, it is determined whether or not the ωI control is being executed by the first arithmetic unit, and A control device for an electric power steering device that continuously executes field-weakening control when it is determined that it is being executed. In the control device of the electric power steering device according to claim 1,
When it is determined that the operation condition of the control is not satisfied during execution of field weakening control by the second calculation unit, when it is determined that execution of ωI control by the first calculation unit is stopped A control device for an electric power steering device that waits for the rotation speed of the motor and the q-axis current value to be less than a specific threshold value, and then cancels execution of field weakening control by the second arithmetic unit. In the control device for the electric power steering device according to claim 1 or 2,
When executing the ωI control by the first arithmetic unit, it is determined whether or not the field weakening control by the second arithmetic unit is likely to be executed, and it is determined that the field weakening control is not likely to be executed Only, the control device of the electric power steering device that executes the ωI control.

Images